1. Field of the Invention
The invention relates to the field of earth boring tools and more particularly to rotating drag bits used in shale or highly plastic formations.
2. Description of the Prior Art
Drilling in shales or plastic formations with a drag bit has always been difficult. The shale, under pressure and in contact with hydraulics, tends to act like a sticky bubble-gum-like mass, sometimes referred to as gumbo, which balls and clogs the bit. Once the bit balls up, it ceases to cut effectively.
Barr et. al., "Improvements in or relating to rotary drill bits," UK Patent GB 2 181 173 A shows a bladed drag bit with a plurality of cutters on each blade in combination with a nozzle which creates a vortex flow having a peripheral stream extending across the cutting elements and exiting into a gage region. However, the cutters are spaced cutters and the nozzle is azimuthally disposed in front of the blade. The flow from each nozzle is isolated from the flow of other nozzles in the bit by the solid mass of the adjacent blades. This is likely to result in isolation of the hydraulics of each vortex pattern, presents a noncutting bit surface between the cutters to the sticky formation, and does not provide for a directed hydraulic impingement on the chips which has any tendency to peel the adhesive chips from the cutter face.
Numerous solutions have been attempted involving large cutters, aggressive cutting patterns, aggressive hydraulics and directed hydraulics all in an attempt to prevent adhesion of the chips to the bit face.
While many of the prior art attempts have been successful in one degree or another, efficient drilling rates have always been difficult to achieve consistently in all types of plastic formations, with all types of hydraulic formulations and in all types of drilling conditions.
Therefore, what is needed is a bit design for use in shale or plastic formations which is highly efficient in a broad range of conditions and environments.